Plants in the Cymopterus genus are often collectively known as spring parsleys. There are approximately 35 – 50 varieties of stemless perennial herbs that grow close to the ground throughout western North America. They are a different plant than the parsley we typically use as a culinary ingredient (Petroselinum crispum), although both are in the Apiaceae family, and can contain a type of chemical compound called furanocoumarins. These compounds can cause severe photosensitivity in extremely high doses.

Spring parsleys are plants in the Cymopterus genus, separate from the type of parsley usually found in the kitchen. Both parsley and spring parsley can become cause photosensitivity in massive doses.

Furanocoumarins are found in a number of plants and can cause reactions either when eaten, or when the compounds come into contact with the skin. Symptoms of photosensitivity from furanocoumarins include:

Skin blistering and peeling are more common with dermal contact, and reactions often are delayed until the skin or eyes are exposed to the ultra-violet rays of the sun.

Types 

Parsley and spring parsley are not the only plants that can contain the furanocoumarins that cause the photosensitivity. They are found mainly in the Apiaceae (celery) and the Rutaceae (citrus) families of plants. Not all of the species in these families contain the furanocoumarin, for instance, sweet oranges such as Valencia and navel oranges, do not include furanocoumarin, whereas citrus fruits such as limes and grapefruit have increased concentrations of the compounds. Some of the plants that do contain this substance include:

Spring parsley plants contain various furanocoumarins such as oxypeucedanin and isoimperatorin. These compounds are a subcategory of psoralens, and are photodynamic, absorbing long-wave ultraviolet radiation that skin may be exposed to. When the furanocoumarins are activated by sunlight, they can damage the cells by inhibiting the synthesis of DNA. This can cause blistering and peeling of the skin affected by the furanocoumarins as well as possible damage to eyes, including corneal damage that can lead to blindness.

Your veterinarian will question you regarding factors that will help to pick the most effective treatment plan for spring parsley ingestion. This information may include issues such as the amount of plant material ingested, how long ago it was eaten, and what part of the plant was consumed. Although the furanocoumarins are found throughout the plant, the concentrations are highest in the seeds and sap of the plant.

If the toxin is unknown because the ingestion or skin contact was not witnessed, a urinalysis, blood chemistry profile, and complete blood count will be required to uncover toxin is causing your pet’s distress. Skin reactions will be evaluated, and your veterinarian might choose to do a skin scraping to rule out other types of infestations or infections, such as staph infection or skin mites.

Any part of the skin that has been subjected to the oil or sap of a plant in the Cymopterus family should be washed immediately to remove any residue then covered to avoid exposure to the sun. A mild soap and clean water should be used, and skin should be dabbed or patted dry rather than rubbed. The dog should immediately be moved indoors or into the shade. If the ingestion of large quantities of the plant material was within the last two to three hours, then your veterinarian may choose to induce vomiting or perform a gastric irrigation in order to physically eliminate as much of the toxin from the digestive system of the patient as possible. Activated charcoal will generally be administered at that point to prevent any further absorption of the toxic compound into the bloodstream. There is no antidote for furanocoumarins, making treatment other than decontamination largely supportive even for ample helpings of the plant. 

Supportive treatments for any type of poisoning generally include IV fluids for dehydration as well as combinations of sugars and electrolytes to adjust for any imbalances that might develop. More moderate ingestions of this plant may be manageable from home. Your veterinarian can advise you on whether or not inducing vomiting will be advantageous for your situation.

If no symptoms have occurred, avoiding sunlight for 48 hours will significantly reduce the likelihood that skin damage will develop. If skin damage does occur then corticosteroids, pain medications, and antihistamines may have some success in easing the discomfort. Infections and infestations are also possible, so it is important to keep the skin as clean and free of insects and debris as possible, and antibiotics may be prescribed to either treat or prevent bacterial infections.

Skin damage from photosensitivity usually heals well for canines, however, infections or infestations can occur if the skin is not kept clean. Flies may be attracted to the skin while it is damaged, and will need to be kept away to avoid maggot infestation. Although the initial extreme photosensitivity is reduced after about 48 hours, some sensitivity to the sun may remain. Some reports in humans with furanocoumarin-caused photosensitivity show they may have continued susceptibility for several months. Avoiding direct sunlight, particularly from around 9 am to 3 pm when the most intense UV rays occur, and covering exposed skin with a cloth covering or canine sun block if you can’t avoid exposure, may help prevent a future incident.